patch 8.1.0972: cannot switch from terminal window to next tabpage

Problem:    Cannot switch from terminal window to next tabpage.
Solution:   Make CTRL-W gt move to next tabpage.
diff --git a/src/window.c b/src/window.c
index c4b543d..83e3e9f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -67,7 +67,7 @@
 static char *m_onlyone = N_("Already only one window");
 
 /*
- * all CTRL-W window commands are handled here, called from normal_cmd().
+ * All CTRL-W window commands are handled here, called from normal_cmd().
  */
     void
 do_window(
@@ -584,6 +584,10 @@
 			nchar = xchar;
 			goto wingotofile;
 #endif
+		    case 't':	    // CTRL-W gt: go to next tab page
+			goto_tabpage((int)Prenum);
+			break;
+
 		    default:
 			beep_flush();
 			break;